The subjunctive....

[hola]

is it a rule or is there some logical reason to the fact that you must go to the subjunctive in hypothetical situations? (if you say "i wish" or if you use the word "if" and things like that)

[tacuba]

That's quite a bit of ground to cover. Why don't you take a look at this link, it may clear up some confusion:

http://www.lingolex.com/swom/wom-subj.htm

[Rusty]

The word 'if' doesn't always necesitate the subjunctive, but 'I wish' does.

In general, if the situation in the subordinate clause is viewed as something hypothetical or anticipated —rather than completed, habitual, or factual— the subjunctive is required.